The new bars of Dairy Milk stay completely solid even when exposed to temperatures of 104F for more than three hours.
Scientists at Cadbury’s research and development plant in Bourneville, near Birmingham, call their breakthrough "temperature-tolerant chocolate."
Two Cadbury engineers have set out the method for making it in an 8,000-word patent application.
While standard chocolate has a melting point of 93F, the new bars are ideal for warmer weather. However, British chocoholics will not benefit from the discovery.
The firm, controversially taken over by American food group Kraft in 2010 in an £11.5 billion deal, insists the new recipe will be available only in hot countries, likely to include India and Brazil.
The secret to the new bars is a change in the so-called "conching step," where a container filled with metal beads grinds the ingredients, which usually include cocoa butter, vegetable oils, milk and sugar.
Cadbury has developed a way of breaking down sugar particles into smaller pieces, reducing how much fat covers them and making the bar more resistant to heat. In its patent application, Cadbury states, "We have found that it is possible to instil temperature-tolerant properties by refining the conched chocolate after the conching step.
"Production of temperature-tolerant chocolate would allow production of chocolate-containing product more suitable for hot climates, particularly in less economically developed countries where the supply chain is ill-equipped to handle temperature fluctuations."
However, the firm’s decision not to sell the new bars in the UK has been blasted by critics as another bitter blow for an iconic British brand.
Robert Halfon, Conservative MP for Harlow, said: ‘Kraft promised British chocolate for British people when they took over Cadbury.
"But it seems that we do all the innovating, then they give the best of British to people overseas.
"This is incredibly disappointing. We invented this brand and now British workers are not being allowed to enjoy the chocolate of their labors. I would urge them to reconsider this and allow British people to have same rights as chocolate-eaters in other countries."
At the time of the Kraft takeover, more than 20,000 readers backed The Mail on Sunday’s campaign to "Keep Cadbury British." Angus Kennedy, a chocolate-taster for over 30 years, said, "What do kids do with chocolates? They put them in their pockets, where they melt and it ends up all over them.
"I think such a product would be very popular here. There’s no reason why it couldn’t be a seasonal product for the warmer months.
"We also eat far more chocolate in this country than in most other places. So we should get the benefits when they come up with new innovations."
Felicity Loudon, a descendant of the founder of Cadbury, said, "Kraft is an American company, so we shouldn’t be surprised that they are leaving us out. It is sad."
Tony Bilsborough, head of corporate affairs at Kraft Foods, said, "It is not something we need in countries like the UK where heat-damaged chocolate is a very rare occurrence, and storage is as it should be.
"Cadbury’s is capable of dealing with the temperate UK climate and there are no plans to use any new recipe. There’s just not a market for it in the UK."
Meanwhile, professional chocolatiers said they were unimpressed with Cadbury’s new invention, claiming it would not taste as good as original Dairy Milk.
Willie Harcourt-Cooze, chocolate-maker and star of Channel 4 fly- on-the-wall documentary Willie’s Wonky Chocolate Factory, said, "There’s no doubt that it will affect the taste. I can’t see why you would develop a product that is less good than the one you already have."
Malachy McReynolds, managing director of Elizabeth Shaw, one of the country’s biggest and oldest chocolate companies, said, "The melt-in-the-mouth characteristics are precisely what makes chocolate so comforting and delightful to eat.
"The pleasure of eating it will inevitably be affected. We would not make our chocolate this way."
Bilsborough, from Kraft Foods, admitted that the new bars would not have the same melt-in-the-mouth quality as normal Dairy Milks.
He said, "The melting point is what makes the bar so attractive, as that is what releases the flavor. If it melts at a higher temperature, it will take longer for it to melt in the mouth."